Aqueous systems, such as for example coatings containing emulsion polymer binders, typically employ thickeners to obtain the desired degree of viscosity needed for the proper formulation and application of the aqueous system. One general type of thickener used in aqueous systems is referred to in the art by the term "associative". Associative thickeners are so called because the mechanism by which they thicken is believed to involve hydrophobic associations between the hydrophobic species in the thickener molecules themselves and/or with other hydrophobic surfaces. A number of different types of associative thickeners are known including, but not limited to polyurethanes, hydrophobically modified alkali soluble emulsions, hydrophobically modified hydroxyethyl cellulose or other natural products, and hydrophobically modified polyacrylamides.
Certain of these associative thickeners, such as for example the polyurethane thickeners, are sold as aqueous solutions containing organic cosolvents. The function of the organic cosolvent, such as for example propylene glycol, is to suppress the viscosity of the aqueous solution containing the associative thickener to allow for ease in its handling before its use as a thickener. While these organic cosolvents perform their intended function, they possess potential environmental, safety and health disadvantages. Viscosity suppression may also be accomplished by the use of surfactants. While this presents no specific health/environmental hazard, it does degrade formulation performance.
It would therefore be advantageous if one could develop more environmentally acceptable and safe materials which could be used in place of these organic cosolvents or surfactants.